1. Lectin-like receptors on murine pulmonary alveolar macrophages which bind to Aspergillus fumigatus conidia in vitro were found to be inhibited by attaching macrophages to glass surfaces coated with saccharides. The most inhibitory saccharides were those which are also known to inhibit the mannose-fucose receptor and chitotriose, a component of chitin. In studies using fluid-phase inhibitors, the monoclonal antibody against a macrophage surface antigen, designated F4/80, was found to be an effective inhibitor of the conidia receptor on macrophages. 2. In studies of the new allylamine antifungal drug, terbinafine (SF 86-327), absorption after oral administration to mice was found to be greatly enhanced by dissolving the drug in 1% Tween and 5% DMSO. One patient was studied after 20 months of receiving this drug. Half-life of plasma clearance was strikingly slow, being 50 days. 3. Purification of the Aspergillus fumigatus complement inhibitor was facilitated by the discovery of anionic properties on ion exchange chromatography. In other studies on fungal opsonins, deposition of the third component of complement on Cryptococcus neoformans in normal human serum was much less in the variety gattii. This may help explain the poorer host defenses, as found in the slower response to chemotherapy among patients infected by this variety. Complement fragment C1q was found to enhance phagocytosis and killing of opsonized C. neoformans blastospores by human monocytes. It is feasible that this interaction may contribute to host defense against cryptococcosis. 4. Improvement in the rapid chemical assay of flucytosine in serum has been achieved using a deaminating enzyme. Ammonia release can be measured by automated techniques. Application for patenting this device has been made.